It’s easier to open an app on my phone, and I believe wholeheartedly that Robinhood works hard to make their UI/UX as “fun” (dopamine-releasing) as possible. One area where Robinhood would be easier than any web app is biometric authentication. Not even having to sign in to the app makes it that much faster and easier to get a dopamine hit from placing a trade.
Robinhood makes their app fun to use with things like swiping up to place the trade, sometimes they put confetti on the screen… it really has quite a lot in common with an actual phone game like Monopoly Go or Candy Crush.